MapReduce高可用性的研究与优化

为提高MapReduce的可用性,提出一种分布式Jobtracker节点模型的优化方案。对Hadoop的核心技术之一MapReduce编程模型中的作业调度过程进行研究分析,指出单一Jobtracker带来的性能瓶颈,提出相应的优化方案;在此基础上,建立总体设计模型,将原MapReduce中单一的Jobtracker节点优化为具有多个Jobtracker节点的Jobtracker集群;在该模型的基础上,采用多对多的通信方法优化通信方式,以维护作业量列表的方式优化作业均衡,提高MapReduce的可用性和作业执行效率。通过测试系统的容错性和执行效率,验证了优化后模型的高可用性和高效性。     

MapReduce能耗建模及优化分析

云计算中心规模的不断扩大以及设计时对能耗因素的忽略,使其日益暴露出高能耗低效率的问题.为提高MapReduce框架能耗利用率,首先对MapReduce任务进行了能耗建模,提出基于CPU利用率估算、主要部件能耗累加及平均功耗估算的任务能耗模型,并在此基础上建立了MapReduce作业能耗模型.其次,基于能耗模型对能耗优化进行了分析,提出从优化MapReduce作业执行能耗、减少MapReduce任务等待能耗与提高MapReduce集群能源利用效率3个方向对MapReduce进行能耗优化.再次,提出异构环境下的数据放置策略减小MapReduce任务等待能耗,提出截止时间约束下的最小资源分配方法提高MapReduce作业能耗利用效率.通过大量的实验及能耗数据分析,验证了能耗模型及能耗优化方法的有效性.     

基于Hadoop框架的MapReduce计算模式的优化设计

对某高校教学资源平台的海量日志进行了分析,将传统单机分析处理模式,转变为Hadoop框架下的MapReduce分布式处理模式。MapReduce采用分而治之的思想,很好地解决了单机对海量数据处理产生的瓶颈问题。通过分析Hadoop源码的使用,认真研究MapReduce对海量数据处理作业流程分析,提出了MapReduce分布式作业计算的优化策略,从而更好地提高了海量数据的处理效率。     

Hadoop MapReduce短作业执行性能优化

Hadoop MapReduce并行计算框架被广泛应用于大规模数据并行处理.近年来,由于其能较好地处理大规模数据,Hadoop MapReduce也被越来越多地使用在查询应用中.为了能够处理大规模数据集,Hadoop的基本设计更多地强调了数据的高吞吐率.然而在处理对短作业响应性能有较高要求的查询应用时,Hadoop MapReduce并行计算框架存在明显不足.为了提升Hadoop对于短作业的执行效率,对原有的Hadoop MapReduce作出以下3点优化：1)通过优化原有的setup和cleanup任务的执行方式,成功地缩短了作业初始化环境准备和作业结束环境清理的时间;2)将首次任务分配从“拉”模式转变为“推”模式;3)将作业执行过程中JobTracker和TaskTrackers之间的控制消息通信从现有的周期性心跳机制中分离出来,采用即时传递机制.最后,采用一种典型的基于MapReduce并行化的查询应用BLAST,对优化工作进行了评估.各种不同类型BLAST作业的测试实验表明,与现有的标准Hadoop相比,优化后的Hadoop平均执行性能提升约23%.     

基于机器学习的MapReduce资源调度算法

针对MapReduce中允许map和shuffle阶段重叠的优化模型需要自适应性的问题,提出了基于此模型的机器学习的资源调度算法,利用贝叶斯分类器依据作业对系统资源的需求和系统环境的匹配程度对作业进行调度,并不断更新分类器,使其具有自适应性,考虑了map和shuffle的重叠阶段。通过模拟实验验证,改进后的算法能够提高MapReduce系统的性能,获得更好的平均响应时间。     

非均匀数据分布下的MapReduce连接查询算法优化

MapReduce分布式计算框架有助于提升大规模数据连接查询的效率,但当连接属性分布不均匀时,其简单的散列策略容易导致计算节点间负载不均衡,影响作业的整体性能。针对连接查询操作中的数据倾斜问题,研究了MapReduce框架下大规模数据连接查询操作的优化算法。首先对经典的改进重分区连接查询算法进行实验分析,研究了传统MapReduce计算框架下连接查询操作的执行流程,找出了基于MapReduce计算框架的连接查询算法在数据分布不均匀时的性能瓶颈;进而提出了组合分割平衡分区优化策略,设计并实现了基于组合分割平衡分区优化策略的改进型连接查询算法。实验结果表明,提出的优化策略在大规模数据的连接查询处理上很好地解决了数据倾斜带来的性能影响,具有好的时间性能和可扩展性。     

基于MapReduce工作流优化器的研究

对MapReduce工作流的优化主要是通过对MapReduce栈的优化实现的。针对MapReduce工作流的优化问题,首先,提出相关概念;其次,介绍MapReduce工作流基于成本的优化过程;然后,通过实例阐述MapReduce工作流中的数据流依赖和资源依赖关系。基于此,提出3种MapReduce工作流优化器,并对其进行端对端的评估。最后,通过实验评估工作流优化器的优化开销并对比分析了这3种工作流优化器。     

面向MapReduce计算模式的中间数据通信优化

针对MapReduce计算模式在Map阶段结束后会产生海量中间数据,导致存在大量跨越机架交换机的数据通信问题,提出一种优化Map密集型作业的中间数据通信优化方法。首先,提取MapReduce计算作业的运行前调度信息的特征并且量化数据通信活跃度;然后,采用朴素贝叶斯分类模型实现分类预测,将历史作业的运行数据作为样本来训练分类模型;最后,根据作业分类预测结果把通信活跃的作业集中映射到同一机架中,通过提高通信局部性来优化性能瓶颈。实验结果表明,所提方案对Shuffle子过程稠密的作业优化效果明显,能够提高4%~5%的计算性能;此外,在多用户运行情况下能降低4.1%中间数据通信延迟。所提方法可有效降低大数据计算过程中的通信延迟,提高异构集群的计算性能。     

Hadoop视角下的Nutch爬行性能优化

通过对Nutch MapReduce job配置参数调优而优化Nutch爬行性能。以Hadoop视角梳理Nutch爬行过程,并基于此详细分析Nutch MapReduce job的工作流特性;对Nutch爬行时MapReduce job进行持续监测,生成优化参数并代入下一轮相同类型的job运行中,从而达到优化目的;通过选取合适的间隔监测值平衡集群环境误差和监测负载以改进优化效果。经过实验测试,Nutch的爬行性能提高了5%~14%,且当监测间隔值为5时有最好优化效果     

基于大数据处理平台的计算任务调度的配置优化

研究介绍了基于大数据处理平台的MapReduce编程模型,并分别从单个计算机任务执行中资源配置问题及多个计算机任务执行相关资源配置优化问题进行全面分析,并通过实例分析了资源配置对MapReduce计算任务执行情况的影响,实践证明,其能够提升MapReduce计算任务性能.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.